Many industrial operations, including chemical processing, gas stream cleansing and the like make use of so-called exchange columns or exchange towers.
For certain applications, processing towers are provided with layers of packing material and arrangements are made for the counterflow through the tower of gas, in one direction, and liquid medium, in the other direction. The packing material is designed to provide for an optimum degree of contact between the counterflowing fluids so that, for example, a particular component of the gas stream may be absorbed into the counterflowing liquid stream.
As will be readily understood, achieving optimum characteristics for the packing material requires the efficient balancing of two somewhat mutually inconsistent characteristics. Thus, on the one hand, it is desired for the gas and liquid to have maximum surface contact with each other, which in turn involves the breaking up of the fluid flow into a maximum number of individual flow paths. At the same time, it is important to minimize resistance to the flow of fluid through the treating tower, so as to avoid excessive energy usage in the conducting of the tower processing operations.
A uniquely advantageous material for use in mist elimination and tower packing applications is described and claimed in U.S. Pat. No. 4,022,596, granted to George C. Pedersen. The Pedersen patent discloses a fabric-like material of a special woven construction, arranged to have a relatively deep waffle-like configuration and in which the individual strands of the woven structure establish a uniquely optimized flow path. Conventionally, the material of the Pedersen patent has been used in layers, oriented across the direction of flow through the processing tower, so that all strands of the material are oriented at 90% to the general direction of fluid flow through the tower. The packing material of the Pedersen patent has enjoyed a high degree of commercial success and is one of the premier products currently available for this purpose.
Notwithstanding the highly optimized characteristics of the packing material of the Pedersen patent, the present invention enables markedly and surprisingly superior results to be achieved in the use of the material of the Pedersen patent, and, indeed, in the use of materials which, while possibly outside the scope of the Pedersen patent, and not incorporating all of its inventive features, are otherwise constructed in a manner to have predetermined related characteristics, to be described further herein.
One of the significantly advantageous characteristics of the material of the Pedersen patent is its extremely high void fraction, consistently above 80% and more typically above 90%, which provides minimum resistance to countercurrent fluid flow through a processing tower, thus minimizing energy usage to create the necessary flow conditions. A concomitant of such high void fraction, however, is the possibility of channeling of the fluid flow to the packing cartridges. That is, a tendency for the fluid flow to concentrate in certain areas, and not utilizing the entire area of the cartridge as uniformly as desired.
The present invention involves a reorientation of the fabric-like material such that the monofilament strands of which it is constructed, originally contemplated to be oriented at 90.degree. to the fluid flow, are reoriented by stacking the fabric-like material on edge, rather than flat. In one particularly preferred embodiment, sections of the fabric are slit into strips, at approximately 45.degree. to the strand orientation (referred to as 45/45 orientation). When the strip-like sections are placed on edge, all of the strands are oriented at approximately 45.degree. to the direction of fluid flow. This is shown to have a remarkable and surprising effect in terms of distributing the fluid flow in a highly uniform manner over the whole surface area of the cartridge. Important advantages can also be achieved with the strip-like sections cut at different angles, even as far as parallel to one set of the strands (referred to as a 90-0 orientation). In this arrangement, one set of strands is parallel to the fluid flow, while the other is at 90.degree. thereto.
Pursuant to the invention, a tower packing cartridge is formed by slitting or otherwise preparing fabric-like material of predetermined characteristics into relatively narrow, strip-like sections, which are placed on edge and assembled in face-to-face contact. Among other characteristics of the material is that it is substantially non-nestable, so that the assembled packing cartridge retains substantially the extremely high void fraction of the fabric itself.
While it is known to orient fabric-like packing material on edge, for example in the Ellis, et al. U.S. Pat. No. 3,243,170, the benefits thereof are not evident in or realized by the structure of the Ellis, et al. patent, because it utilizes a knitted fabric structure, in which the yarn strands are effectively randomly oriented, because of the loop structure of the knitted stitches. Indeed, in the arrangement of the Ellis et al. patent, knitted material is crimped and then doubled back and forth upon itself, so that the crimping lines of two adjacent faces cross each other. This perhaps is intended to emulate known corrugated structures, such as shown in the Huber U.S. Pat. No. 3,285,587, for example, in which packing material is made up of an assemblage of corrugated plates, with adjacent sets of corrugations being inclined in opposite directions.
For a more complete understanding of the above and other features and advantages of the invention, reference should be made to the following detailed description of a preferred embodiment and to the accompanying drawings.